Recent imaging devices are expected to become smaller in size, while being expected to have a larger number of pixels, higher image quality, and a higher processing speed. As an imaging device that satisfies such demands, a layered imaging device has been suggested (see Patent Document 1, for example).
In a layered imaging device, a chip having a signal processing circuit formed thereon, instead of a supporting substrate for an imaging device, is used, and the pixel portion is overlapped on the chip. It is suggested that an imaging device can be made smaller in size with such a structure.